The availability of genetic analysis and transgenic techniques in the mouse have led to its widespread acceptance as the preferred animal model for studying mammalian development and many human diseases. The basic limitation for studying development in the mouse, or any other mammal, is the inaccessibility of the embryos which are encased in the maternal uterus. Recently, several groups have developed methods to inject cells and lineage-tracing viruses into the lateral forebrain ventricles of rat and mouse embryos at relatively late stages of embryogenesis (mouse gestational age 12.5 days, E12.5 or later) but these injections are not targeted to specific regions since the cells and viruses are free to move throughout embryonic ventricles before integrating in the brain. Furthermore, much of embryonic brain development has been completed before the agents can be injected. This laboratory has developed a high resolution UBM to visualize mouse embryos, in vivo. Preliminary studies have demonstrated that 40-50 MHZ UBM can be used as a guidance system, allowing targeting injections of cells and retrovirus into the embryonic muse brain and other organs at stages as early as E9.5. The overall goal of this project is to develop instrumentation to improve both the visualization and delivery capability injection system, enabling more accurate targeted injections into live mouse embryos in utero at all stages of development between E8.5 and E13.5 The specific aims are: 1) to produce a set of transducers which optimize the imaging and guidance performance of the UBM for a range of mouse embryonic stages between E8.5 and E13.5; 2) to develop 50 MHz multi- element annular array transducers to improve the UBM image characteristic over a wide depth of field; 3) to implement robust 3 dimensional (3-D) UBM imaging protocols, including real-time 3-D image manipulation, in order to improve the accuracy of site-specific ultrasound-guide injections; and 3) to determine the feasibility of using contrast agents to improve the localization of the infection site. The combination of recent breakthroughs in mouse genetics, together with this state-of-the-art UBM technology, will provide powerful new tools for studying mammalian development and human disease models in the mouse.